The invention relates to a cylindrical printing device including an assembly of a support cylinder, at least one printing sleeve intended to be mounted on the support cylinder, and indexing means for mounting each sleeve on the support cylinder. This cylindrical printing device is referred to here as a xe2x80x9cprinting cylinderxe2x80x9d.
It is known that in order to reduce waste in starting a printing machine, as well as an adjustment time for setting registration of colors, manufacturers of printing sleeves and builders of printing machines propose a system of registration of the printing sleeve on the corresponding carrier cylinder of the printing machine, also commonly called indexing by experts in the field.
This indexing system comprises a recess in the thickness of the printing sleeve and a device that cooperates with the recess, such as a small cylindrical piece, which is attached to the carrier cylinder. This indexing piece generally projects a distance of a few millimeters.
For a sleeve of relatively small thickness, particularly less than 15 mm, the recess can extend through the entire thickness of the sleeve. Thus, this recess, made in a lateral end face of the sleeve, opens onto both the interior wall and the exterior wall of the sleeve.
When the sleeve is thicker, with a thickness greater than 15 mm, in particular, the recess is not generally made through the entire thickness of the sleeve. One rather produces a receptacle in a lateral face of the sleeve that opens onto its interior wall. A key is fit and set in this receptacle, the recess for positioning the indexing device being produced by machining in this key.
Generally, the recess produced in the sleeve for its positioning on the indexing device extends according to a longitudinal generating line plotted on the exterior wall of the printing sleeve, this generating line being used to position the printing plates correctly.
Mounting of a printing sleeve on a carrier cylinder is done by an operator. This operator has to make the indexing device provided on the carrier cylinder enter the recess in the printing sleeve, while this indexing device is necessarily positioned on the side opposite from the operator.
This mounting is difficult, even for sleeves with small web widths, when they must be placed on cylinders in the upper part of the printing machine which are therefore poorly accessible to the operator.
This operation is even more difficult for printing sleeves of relatively large width, particularly greater than 600 mm, above all if the sleeve is very thick. In effect, in this case, the support cylinder with the indexing device is no longer visible to the operator, because of the thickness and the length of the sleeve.
The operator must therefore proceed by trial and error in order to make the recess in the sleeve and the indexing device borne by the support cylinder coincide. Impacts then occur between the printing sleeve and the indexing device.
The printing sleeves are generally mounted on a carrier cylinder by means of pressurized air that is injected at one of the ends of the carrier cylinder and emerges through openings arranged angularly around the cylinder. This creates a cushion of air between the carrier cylinder and the printing sleeve, which causes a slight radial expansion of the sleeve and allows the sleeve to move along and around the support cylinder.
It is possible to refer to the document EP-510744 which describes a support cylinder on which at least one printing sleeve is intended to be mounted.
The support cylinder has as many indexing devices as the number of sleeves, these indexing devices being retractable and capable of projecting from the surface of the support cylinder. This sleeve has, on one of its edges, a hollow in order to cooperate with the corresponding indexing device and in order to mount the sleeve in the appropriate position. Furthermore, mounting of the sleeves is done using a supply of compressed air.
Depending on the structure of the printing sleeves, the air pressure used changes the radial expansion of the sleeve and, by creation of a cushion of air, promotes an often violent propulsion of the printing sleeve, which advances jerkily on the carrier cylinder. Thus, when the recess of the sleeve is not aligned with the indexing device provided on the support cylinder, the sleeve knocks against it, which causes rapid deterioration of the face of the printing sleeve that has the recess.
This deterioration makes the printing sleeve unusable after a few mounting operations. The printer must then true the deteriorated face in order to eliminate any trace of the repetitive impacts, such as indentations and raised parts.
It is also appropriate to note that between two uses, the sleeves are stored with one face resting on the floor. These sleeves are not always handled with care, which leads to impacts to and deformations of the face resting on the floor, all the more since the sleeves are heavy and the floor often contains uneven places and even waste.
Finally, mounting of each sleeve is done by trial and error, above all when the support cylinder intended to receive the sleeve is not very accessible, and the sleeve is very large and heavy.
This mounting therefore takes a relatively long time, which increases the loss of printing time that is sentimental to a printer.
The invention aims to offset these disadvantages and to facilitate the work of the operators by proposing a printing cylinder with a sleeve having a ring that protects the cylinder from possible impacts and that can also be used for guidance during mounting of the sleeve.
Thus, the invention relates to a printing cylinder that includes a support cylinder, at least one printing sleeve intended to be mounted on said support cylinder, and means of indexing each sleeve on the support cylinder, the indexing means including a recess or the like on a lateral face of the sleeve, and at least one indexing device borne by the support cylinder and that projects from it, the recess and each indexing device being intended to cooperate in order to mount the sleeve on the support cylinder while registering it. The printing sleeve has at least one ring in the extension of its interior wall and which at least in part projects from the lateral face, so that the ring, in which the recess or the like is present, protects the sleeve from impacts between it and the indexing device during mounting of the printing sleeve on the support cylinder.
In a first embodiment variant, the ring is produced in the form of a single piece together with the sleeve, in particular by machining.
In a second embodiment variant, the ring is a piece that is connected on or in the sleeve, particularly by adhesive bonding, by crimping, or by direct molding.
In this case, the ring is produced from an elastic and shock absorbing material, such as aluminum or a plastic material such as polyamide, PTFE (polytetrafluoroethylene), polycarbonate, PU (polyurethane), PES (polyether sulfone), or PE (polyethylene).
Preferably, the ring includes means of guiding the indexing device borne by the support cylinder towards the recess in the ring.
The guidance means advantageously includes two inclines, arranged on opposite sides of the recess, each of the inclines extending from the recess to the exterior edge of the ring.
Preferably, these inclines are symmetrical with respect to the recess.
particular, they can be helical or linear.
Each incline corresponds to an angle which is advantageously between 25 and 60xc2x0, and is preferably equal to 45xc2x0.
Preferable a stop is provided between the exterior, edge of the ring and the end of at least one incline, at an end opposite from the recess.
The printing sleeve of the cylinder according to the invention advantageously includes a ring with a recess on each of its lateral faces, so that it can be reversibly mounted.
In order to facilitate the work of the operators, the printing sleeve has, on a lateral face opposite the lateral face including the ring, and which is intended to be visible to an operator during mounting of the sleeve on the support cylinder, means of visualizing the corresponding location of the recess, and, possibly, the means of guidance, on the face of the sleeve that has the ring.
The printing sleeve of the printing cylinder according to the invention can have means of visualizing each of its lateral faces, for reversible mounting.
The printing sleeve advantageously has, on its exterior wall, integrated guides for installation and cutting using a cutting tool of a stereotype plate and/or double sided adhesive placed on the sleeve.
In one embodiment of the printing cylinder, the support cylinder has several indexing devices, which are at least in part retractable.
The indexing devices of the support cylinder can be arranged according to a generating line of the support cylinder.
Finally, an intermediate sleeve can be already arranged on the support cylinder before mounting of the printing sleeve. In this case, the indexing devices are positioned on the exterior surface of this intermediate sleeve.